1. Field of the Invention
The present invention relates to a method of and an apparatus for controlling a machine tool to restart its automatic operation for machining a workpiece from an interrupted point after the machine tool, which has been automatically operated by NC (Numerical Control) program commands output from an NC apparatus, is caused to interrupt its automatic operation.
2. Description of the Related Art
Japanese published patent application No. 2000-35815 discloses a numerically controlled machine tool. The disclosed machine tool performs a sequence of machine motions such as for a tool changing process with a single sub-command (auxiliary command). After the execution of the sub-command is interrupted due to a fault during the sequence of machine motions, the numerically controlled machine tool can subsequently restart the execution of the sub-command.
Specifically, when the execution of the sub-command, which is described in a machining program, is interrupted while the sub-command is being executed, then the operator determines whether the sub-command needs to be corrected or not in order to restart the execution of the sub-command.
If the sub-command needs to be corrected, then the operator corrects the sub-command. However, correcting the sub-command requires the operator to have a certain level of skill, and has been burdensome for the operator.